A nuclear reactor pressure vessel, as exemplified by a pressurized-water reactor, has a substantially cylindrical side wall closed by a bottom and a top which is normally a removable cover. The vessel is vertically positioned in a concrete reactor pit with the vessel's bottom supported directly or indirectly by the pit's bottom. The top of the vessel has struts, swinging hooks, etc., connecting it with the top rim of the concrete pit and designed to hold the vessel's top against upward movement when the vessel is thermally expanded axially. The design of the top holding means is such that when the vessel is thermally contracted, meaning it is cold, the top holding means are loose as required to permit removal of the vessel's cover, for example, the looseness disappearing as the vessel axially expands when the reactor is started up, so that at the vessel's operating temperature the vessel is rather highly stressed under compression in its axial direction, reducing the risk for a wall rupture due to the coincidental axial expansion involved. The dimensions of the pit are, of course, designed relative to the dimensions of the vessel to accommodate the vessel's expansion and contraction.
It follows, that when the vessel is at its operating temperature, it is highly stressed in its axial direction with its bottom exerting great force against the bottom of the pit. At the same time, the bottom of the vessel must be free to radially expand and contract.
In view of the above, various arrangements have been proposed for transmitting the stress from the bottom of the vessel to the bottom of the pit. These have contemplated the use of anti-friction bearing arrangements, horizontal sliding bearings, etc. They have all had undesirable features such as complicated design, large manufacturing and installation cost, and, possibly, unreliability under the severe surface conditions of heat and high stressing inherent to the conditions under which they must operate in the pit between the latter's bottom and the bottom of the axially stressed vessel during the operation of the reactor.